Manipulating Strings in Java

Encoding Quick Response Code in Java Manipulating Strings

Most likely, you won t have any idea, but you don t have to because you can calculate the square root of a number just by using that language s built-in square root math function So if you wanted to know the square root of 34 and store it in an Answer variable, you could just use the sqrt math function, such as

Answer = sqrt(34)

In some languages, such as BASIC, it doesn t matter if you type a math function in either uppercase or lowercase In other languages, such as C, commands like SQRT and sqrt are considered two completely different functions, so you must know if your language requires you to type a math function in all uppercase or all lowercase Table 3-4 lists some common built-in math functions found in many programming languages

Table 3-4

abs (x) cos (x) exp (x) log (x) sqrt (x)

Finds the absolute value of x Finds the cosine of x Returns a number raised to the power of x Finds the logarithm of x Finds the square root of x

abs ( 45) = 45 cos (2) = 041614684 exp (3) = 200855369 log (4) = sqrt (5) = 138629436 223606798

x = 67 * cos (5) + sqrt (7)

Rather than plug fixed values into a math function, it s more flexible just to plug in variables instead, such as

Angle = 5 Height = 7 X = 67 * cos (Angle) + sqrt (Height)

Just as math operators can manipulate numbers, so can string operators manipulate strings The simplest and most common string operator is the concatenation operator, which smashes two strings together to make a single string

Most programming languages use either the plus sign (+) or the ampersand (&) symbol as the concatenation operator, such as

$Name = Joe Smith ;

In the preceding examples, the concatenation operator takes the string Joe and combines it with the second string Smith to create a single string that contains Joe Smith When concatenating strings, you may need to insert a space between the two strings Otherwise, the concatenation operator smashes both strings together like JoeSmith , which you may not want For more flexibility in manipulating strings, many programming languages include built-in string functions These functions can help you manipulate strings in different ways, such as counting the number of characters in a string or removing characters from a string Table 3-5 lists some common built-in string functions found in many programming languages Not all programming languages include these string functions, and if they do, they ll likely use different names for the same functions For example, Visual Basic has a Trim function for removing characters from a string, but Perl uses a substr function that performs the same task

Table 3-5

length (x) trim (x, y) index (x, y) compare (x, y) replace (x, y, z)

Counts the number of characters in a string (x), including spaces Removes characters from a string Returns the position of a string within another string Compares two strings to see if they re identical Replaces one string from within another

length (Hi there!) = 9 trim (Mary, 1) = ary index (korat, ra) = 3 compare (A, a) = False replace (Batter, att, ik) = Biker

Before you can manipulate a string, you first must find it Although some programming languages include string searching functions, most of them are fairly limited to finding exact matches of strings To remedy this problem, many programming languages (such as Perl and Tcl) use regular expressions (A regular expression is just a series of symbols that tell the computer how to find a specific pattern in a string) If a programming language doesn t offer built-in support for regular expressions, many programmers have written subprogram libraries that let you add regular expressions to your program By using regular expressions, your programs can perform more sophisticated text searching than any built-in string functions could ever do